Natural gas is regarded as fuel that places less load to the environment compared with petroleum-based fuel because, when combusted, natural gas gives off neither sulfur oxide nor particulate substances that contaminate the atmosphere and produces less carbon dioxide per unit amount of generated heat. Further, natural gas can be distributed and used at room temperature, which provides an advantage of easy handling.
For this reason, natural gas is increasingly attracting attention as alternative fuel that can replace petroleum in the field of energy supply because solutions to the environment problem are urgently being looked for and diverse resources are required all over the world.
In the process of producing synthetic hydrocarbons such as naphtha, kerosene and gas oil by way of chemical reactions, using natural gas as raw material, generally synthesis gas (mixture gas of carbon monoxide and hydrogen) is produced as intermediate by a reforming reaction.
When producing synthesis gas, firstly the sulfur compounds contained in the natural gas to be used as raw material are removed in a desulfurization apparatus. Then, steam and/or carbon dioxide is added to the desulfurized natural gas and subsequently the desulfurized natural gas is introduced into a synthesis gas production apparatus and heated in a reformer. As a result, a reforming reaction proceeds in the reformer due to catalysis of the reforming catalyst filled in the reformer to thereby produce synthesis gas. While a steam reforming method using steam is mainly employed for the reforming reaction, a carbon dioxide reforming method using carbon dioxide has been put to practical use in recent years. A carbon dioxide reforming method does not require removal of the carbon dioxide contained in natural gas before a reforming reaction and hence provides an advantage of raising the efficiency of synthesis gas production process and reducing the synthesis gas production cost. Furthermore, the unreacted and/or produced carbon dioxide contained in the produced synthesis gas can be separated and collected for recycling to the synthesis gas production step so as to be reutilized in the carbon dioxide reforming reaction. Thus, carbon dioxide can be highly efficiently exploited as resource in a carbon dioxide reforming process.
Thereafter, typically, liquid hydrocarbons are produced from the produced synthesis gas by way of a Fischer-Tropsch reaction and synthetic hydrocarbons such as product fuel oil are produced by hydroprocessing the obtained liquid hydrocarbons in a hydrogenation process. The series of steps including a Fischer-Tropsch reaction is referred to as Gas-to-Liquids (GTL) process. Synthesis gas can also be used for methanol synthesis and oxo-synthesis.
Reforming reactions proceed at high temperatures typically between 700° C. and 900° C. in the case of steam reforming, for example. Therefore, the high-temperature synthesis gas that is discharged from the exit of a reformer is fed to a waste heat boiler by way of piping coated with refractory castable for a heat-exchange process.